Cardiovascular autonomic and hemodynamic responses to vagus nerve stimulation in drug-resistant epilepsy

Purpose: Vagus nerve stimulation (VNS) is used as an adjunctive therapy for treating patients with drug-resistant epilepsy. The impact of VNS on cardiovascular autonomic function remains to be fully understood. We determined changes in cardiovascular sympathetic and parasympathetic, and hemodynamic function in association with VNS in patients with drug-resistant focal epilepsy.

Method: Longitudinal (n=15) evaluation of beat-to-beat blood pressure (BP) and heart rate variability (HRV), baroreflex sensibility, and hemodynamic function performed before VNS implantation, 6-months after implantation, and a mean of 12-months after implantation; and cross-sectional study (n=14) of BP and HR variability and baroreflex sensitivity during VNS on and VNS off.

Results: In the longitudinal study, no differences were observed between the baseline, the 6-month visit, and the final visit in markers of parasympathetic cardiovagal tone or baroreflex sensitivity. Systolic and diastolic BP upon 5-min of head-up tilt increased significantly after VNS implantation (Systolic BP: -16.69±5.65mmHg at baseline, 2.86±16.54mmHg at 6-month, 12.25±12.95mmHg at final visit, p=0.01; diastolic BP: -14.84±24.72mmHg at baseline, 0.86±16.97mmHg at 6-month, and 17±12.76mmHg at final visit, p=0.001).

Conclusion: VNS does not seem to produce alterations in parasympathetic cardiovagal tone, regardless of the laterality of the stimulus. We observed a slight increase in sympathetic cardiovascular modulations. These changes had no significant hemodynamic implications. These findings contribute to the understanding of potential mechanisms of action of VNS.